Intermarket sweep orders (ISO) is a type of stock market order that sweeps several different market centers and scoop up as many

shares In financial markets, a share is a unit of equity ownership in the capital stock of a corporation, and can refer to units of mutual funds, limited partnerships, and real estate investment trusts. Share capital refers to all of the shares of an ...

as possible from them all. These work against the order-protection rule under regulation NMS. For example, if a

trader Trader may refer to: * Merchant, retailer or one who attempts to generally buy wholesale and sell later at a profit * The owner of a trading post, where manufactured goods were exchanged with native peoples for furs and hides. * Trader (finance), ...

is trying to buy 1000 shares of X, and there are 100 shares of X being offered at $1 at one exchange and 2000 at $1.10 at another exchange, the order protection rule would let you buy ONLY those 100 shares at $1, after which you would need to send in other orders. With the ISO, you can buy the 100 shares at $1 and the remaining 900 at $1.10 on the other exchange subsequently.

References

Stock market Financial markets {{stockexchange-stub